Blackbody

Q.

What is rayleigh-jeans law on black body radiation and ultraviolet catastrophe?

Q.

What are the uses of specific heat in our daily life?

Q.

An antenna is mounted on a 400 m all building. What will be the wavelength of signal that can be radiated effectively by the transmission tower upto a range of 44 km?

Q. A black body emits radiation at the rate $P$ when its temperature is $T$. At this temperature the wavelength at which the radiation has maximum intensity is ${\lambda }_0$. If at another temperature $T^{\prime },$ the power radiated is $P^{\prime }$ and wavelength at maximum intensity is $\frac{{\lambda }_0}{2}$. If $P^{\prime }{T}^{\prime }=nPT,$ then value of $n$ is

Q.

Electromagnetic radiation with maximum wavelength is?

1. Radiowave

2. X-ray

3. Infrared ray

4. Ultraviolet ray

Q. A polished metal plate with a rough black spot on it is heated to about $1400\text{K}$ and quickly taken to a dark room. The spot will appear

1. darker than the plate surface
2. brighter than the plate surface
3. equally bright as the plate surface
4. equally dark as the plate surface

Q.

Differentiate between heat energy and light energy.

Q.

What is a perfect black body radiation?

Q.

Define infrared radiation and give some examples of It.

Q. A black body radiates heat energy at the rate of $2\times {10}^5{\text{J-s}}^{-1}{\text{m}}^{-2}$ at a temperature of ${127}^{\circ }\text{C}$. The temperature of black body, at which the rate of heat radiation is $32\times {10}^5{\text{J-s}}^{-1}{\text{m}}^{-2}$ is

1. ${873}^{\circ }\text{C}$
2. ${273}^{\circ }\text{C}$
3. ${527}^{\circ }\text{C}$
4. ${927}^{\circ }\text{C}$

Q.

A piece of iron is heated in a flame. It first becomes dull red then becomes reddish yellow and finally turns to white-hot. The correct explanation for the above observation can be obtained using which of the following?

1. Wein’s displacement law

2. Stefan’s law

3. Kirchhoff’s law

4. Newton’s law of cooling

Q. Two solid spheres A and B made of same material have radii Ra and Rb . Both the sphere are cool from the same temp. under the condition valid for Newtons law of cooling . The rate of ratio of change of temperature A and B

Q.

An object is at a temperature of ${400}^0$ C. At what temperature would it radiate energy twice as fast? The temperature of the surroundings may be assumed to be negligible

1. 800°C

2. 800K

3. 200°C

4. 200K

Q. The radiation from the sun, incident normally at the surface of the earth is $20{\text{kcal/m}}^2\text{min}$. What would have the radiant energy, incident normally on the earth, if the sun had a temperature twice of the present one?

1. $80{\text{kcal/m}}^2\text{min}$
2. $320{\text{kcal/m}}^2\text{min}$
3. $160{\text{kcal/m}}^2\text{min}$
4. $40{\text{kcal/m}}^2\text{min}$

Q.

A thin paper cup filled with water does not catch fire when placed over a flame. This is because

1. The water cuts off oxygen supply to the paper cup.

2. Water is an excellent conductor of heat.

3. The paper cup does not become appreciably hotter than the water it contain.

4. Paper is a poor conductor of heat.

Q.

Name the coolant used in car radiators.

Q. The energy radiated by a black body at $2300\text{K}$ is found to have a maximum intensity at a wavelength $1260\text{nm}$, its emissive power being $8000{\text{W/m}}^2$. When the body is cooled to a temperature $T\text{K}$, the emissive power is found to decrease to $500{\text{W/m}}^2$. Find the temperature $T$.

1. $1000\text{K}$
2. $1500\text{K}$
3. $1150\text{K}$
4. $1050\text{K}$

Q.

The wavelength of maximum energy released during an atomic explosion was $2.93\times {10}^{10}m$. Given that Weins constant is $2.93\times {10}^{-3}$ m-K, the maximum temperature attained must be of the order of

1. 

2. 

3. 

4. 

Q. In which one of the following regions of the electromagnetic spectrum will be vibrational motion of molecules give rise to absorption-

1. Ultraviolet
2. Microwaves
3. Infrared
4. Radio waves

Q.

Describe the construction of a thermo flask with the help of a neat diagram and label it.

Q. Some amount of a radioactive substance (half life $=10$ days ) is spread inside a room and consequently the level of radiation becomes $50$ times permissible level for normal occupancy of the room. After how many days the room will be safe for occupation?
[Use, $\ln 50=3.9120$]

Q.

Which method of heat transfer does not need a medium.

1. Conduction

2. Convection

3. Radiation

Q. Regarding X ray spectrum which of the following statement/s is/are true

1. None of these
2. Wavelength of continuous spectrum is dependent on the potential difference scross tube
3. The characteristic X ray spectrum is emitted due to excitation of inner electrons of atom
4. Wavelength of characteristic spectrum depend on the potential difference across the tube

Q. A polished metallic piece and a black painted wooden piece are kept in open in bright sun for a long time. Then,

1. the wooden piece will absorb less heat than the metallic piece
2. the wooden piece will have a lower temperature than the metallic piece
3. when touched, the metallic piece will be felt hotter than the wooden piece
4. when the two pieces are removed from the open to a cold room, the wooden piece will lose heat at a faster rate than the metallic piece

Q. A black body at a temperature of ${327}^{\circ }\text{C}$ radiates $4{\text{cal cm}}^{-2}{\text{s}}^{-1}$ at a temperature of ${927}^{\circ }\text{C}$, the rate of heat radiated per unit area in ${\text{cal cm}}^{-2}{\text{s}}^{-1}$ will be

1. $64$
2. $128$
3. $16$
4. $32$

Q. A copper sphere is suspended in an evacuated chamber maintained at 300 K. The sphere is maintained at a constant temperature of 500 K by heating it electrically. A total of 210 W of electric power is needed to do it. When the surface of the copper sphere is completely blackened, 700 W is needed to maintain the same temperature of the sphere. Calculate the emissivity of copper.

1. 0.5

2. 0.4

3. 0.3

4. 0.2

Q. A black body of temperature T is inside a chamber of temperature $T_0$. Now the closed chamber is slightly opened to sun such that temperature of black body (T) and chamber $\left(T_0\right)$ remains constant

1. black body will absorb more radiation
2. black body will absorb less radiation
3. black body emit energy equal to energy absorbed by it
4. black body emit more energy

Q.

A hole is drilled in a copper sheet. The diameter of the hole is 4.24 cm at 27.0 °C. What is the change in the diameter of the hole when the sheet is heated to 227 °C? Coefficient of linear expansion of copper = 1.70 × 10^–5 K^–1.

Q. The relation between efficiency $\eta$ of a heat engine and the co-efficient of performance $\alpha$ of a refrigerator is:

1. $\eta =\frac{1}{1-\alpha }$
2. $\eta =\frac{1}{1+\alpha }$
3. $\eta =1-\alpha$
4. $\eta =1+\alpha$

Q. Assume that the total surface area of a human body is $1.6{\text{m}}^2$ and that it radiates like an ideal radiator. Calculate the amount of energy radiated per second by the body if the body temperature is ${37}^{\circ }\text{C}$.

Stefan constant $=6.0\times {10}^{-8}\text{W}{\text{m}}^{-2}{\text{K}}^{-4}$.

1. $732\text{J}$
2. $887\text{J}$
3. $993\text{J}$
4. $632\text{J}$